Ladies, there’s a reason we swoon over a guy with great hair. In evolutionary terms, hair can be a sign of sexual dominance. Like a peacock’s colorful plumage, it’s intended to attract the opposite sex (“epigamic,” in science speak). In fact, the males of a certain species of monkey develop seemingly coiffed, human-like patches of hair on their heads during puberty. A lion’s mane is an example of epigamic hair, too, because it’s used to show superiority over rivals on the mating scene.